We present studies of resonance-enhanced photoionization for isotope-selective loading of Ca ϩ into a Paul trap. The 4s 2 1 S 0 ↔4s4p 1 P 1 transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope 40 Ca ϩ . Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170͑60͒ Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species 43 Ca ϩ and 46 Ca ϩ , which have not previously been laser cooled, the loading is not fully isotope selective, but we show that pure crystals of 43 Ca ϩ may nevertheless be obtained. We find that for loading 40 Ca ϩ the 389 nm laser may be replaced by an incoherent source.
We have implemented a universal quantum logic gate between qubits stored in the spin state of a pair of trapped 40 Ca ions. An initial product state was driven to a maximally entangled state deterministically, with 83% fidelity. We present a general approach to quantum state tomography which achieves good robustness to experimental noise and drift, and use it to measure the spin state of the ions. We find the entanglement of formation is 0.54.
We create entangled states of the spin and motion of a single 40Ca+ ion in a linear ion trap. We theoretically study and experimentally observe the behavior outside the Lamb-Dicke regime, where the trajectory in phase space is modified and the motional coherent states become squeezed. We directly observe the modification of the return time of the trajectory, and infer the squeezing. The mesoscopic entanglement is observed up to Deltaalpha=5.1 with coherence time 170 micros and mean phonon excitation n = 16.
We demonstrate sympathetic cooling of a 43 Ca + trapped-ion "memory" qubit by a 40 Ca + "coolant" ion near the ground state of both axial motional modes, whilst maintaining coherence of the qubit. This is an essential ingredient in trapped-ion quantum computers. The isotope shifts are sufficient to suppress decoherence and phase shifts of the memory qubit due to the cooling light which illuminates both ions. We measure the qubit coherence during 10 cycles of sideband cooling, finding a coherence loss of 3.3% per cooling cycle. The natural limit of the method is O(10 −4 ) infidelity per cooling cycle.Trapped ions have been shown to have much promise for quantum information processing (QIP). Multi-qubit quantum logic gates [1][2][3][4][5][6][7], high-fidelity operations [7,8], teleportation and elementary algorithms [9][10][11][12] have been demonstrated. Scaling up from these small scale demonstrations to algorithms involving large numbers of gates, measurements and individual manipulations of a large number of ions is a major challenge [13]. One approach to this problem is to move the ions themselves around a large array of traps. This involves shuttling, separation, and recombination of ion strings, which introduces heating [14]. In addition, ambient heating of ions has been widely observed in ion traps, caused by fluctuations in the electric potential at the ion [15][16][17]. All logic gate schemes demonstrated thus far require the ions to be well within the Lamb-Dicke regime for high-fidelity operation [3,18]. Thus for a quantum processor involving ions in trap arrays, the ability to cool ions near the ground state of motion while preserving the logical information stored in them is essential.One approach to this problem is to cool sympathetically the qubit ion, making use of its Coulomb interaction with another "coolant" ion stored in the same trap [19,20]. Owing to the Coulomb interaction, the normal modes of motion of the ions are shared, therefore by addressing laser cooling only to the "coolant" ion we also cool the logical qubit ion. In order that the light used for cooling does not decohere the qubit(s) stored in the logic ion(s), it is necessary that it couples only weakly to the internal state of the logic ion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.